
    <!DOCTYPE html>
    <html lang="zh-CN">
    <head>
      <meta charset="UTF-8">
      <meta name="viewport" content="width=device-width, initial-scale=1.0">
      <title>优化高并发场景下的数据库查询性能 - 交互式测验</title>
      <style>
        @import url('https://fonts.googleapis.com/css2?family=Noto+Sans+SC:wght@400;500;700&display=swap');
        
        body {
          font-family: 'Noto Sans SC', sans-serif;
          background-color: #f4f7f9;
          color: #333;
          display: flex;
          justify-content: center;
          align-items: center;
          min-height: 100vh;
          margin: 0;
          padding: 20px;
          box-sizing: border-box;
        }
        
        .main-wrapper {
            position: relative;
            width: 100%;
            max-width: 900px; /* Wider to accommodate buttons */
            display: flex;
            justify-content: center;
            align-items: center;
        }

        .quiz-container {
          background-color: #ffffff;
          border-radius: 16px;
          box-shadow: 0 8px 32px rgba(0, 0, 0, 0.1);
          width: 100%;
          max-width: 700px;
          overflow: hidden;
          z-index: 10;
        }

        .quiz-header {
          background-color: #4a90e2;
          color: white;
          padding: 20px 30px;
          text-align: center;
        }

        .quiz-header h1 {
          margin: 0;
          font-size: 24px;
          font-weight: 700;
        }
        
        .quiz-header p {
            margin: 5px 0 0;
            font-size: 14px;
            opacity: 0.9;
        }

        .quiz-body {
          padding: 30px;
        }

        .progress-bar {
            display: none; /* 隐藏进度条 */
            width: 100%;
            background-color: #e0e0e0;
            border-radius: 5px;
            height: 10px;
            margin-bottom: 20px;
        }

        #progress-indicator {
            height: 100%;
            width: 0%;
            background-color: #4caf50;
            border-radius: 5px;
            transition: width 0.3s ease;
        }

        #question-container {
          margin-bottom: 20px;
        }

        #question-text {
          font-size: 18px;
          font-weight: 500;
          line-height: 1.6;
          margin-bottom: 25px;
        }

        .options-list {
          list-style: none;
          padding: 0;
          margin: 0;
        }

        .option-item {
          background-color: #f8f9fa;
          border: 1px solid #dee2e6;
          border-radius: 8px;
          padding: 15px;
          margin-bottom: 12px;
          cursor: pointer;
          transition: background-color 0.2s ease, border-color 0.2s ease;
        }

        .option-item:hover {
          background-color: #e9ecef;
        }
        
        .option-item.selected {
            background-color: #d1e7fd;
            border-color: #4a90e2;
        }

        .quiz-footer {
          padding: 20px 30px;
          display: flex;
          justify-content: space-between; /* 将按钮分布在两侧 */
          align-items: center;
          min-height: 65px; /* Reserve space */
        }

        .nav-btn {
          background-color: #4a90e2;
          color: white;
          border: none;
          border-radius: 8px;
          padding: 10px 20px;
          font-size: 16px;
          font-weight: 500;
          cursor: pointer;
          transition: background-color 0.2s ease, transform 0.2s ease;
          box-shadow: 0 4px 12px rgba(0,0,0,0.15);
        }
        
        #next-btn {
            background-color: #28a745;
        }

        .nav-btn:hover {
          background-color: #357abd;
          transform: scale(1.05);
        }
        
        .nav-btn:disabled {
            background-color: #a0c3e8;
            cursor: not-allowed;
            opacity: 0.7;
        }

        #result-container {
            border-top: 1px solid #eee;
        }
        
        .result-box {
            border-radius: 8px;
            padding: 20px;
            margin-top: 20px;
        }
        
        .result-box.correct {
            background-color: #d4edda;
            border: 1px solid #c3e6cb;
            color: #155724;
        }

        .result-box.incorrect {
            background-color: #f8d7da;
            border: 1px solid #f5c6cb;
            color: #721c24;
        }
        
        .result-box h3 {
            margin-top: 0;
        }

        .explanation-text {
            margin-top: 15px;
            line-height: 1.7;
        }
        
        .source-text {
            font-style: italic;
            font-size: 14px;
            margin-top: 15px;
            color: #555;
        }

        
        .final-score-container {
            padding: 40px;
            text-align: center;
        }
        .final-score-container h2 {
            margin-top: 0;
            margin-bottom: 30px;
        }
        .score-summary {
            display: flex;
            justify-content: center;
            gap: 20px;
            margin-bottom: 40px;
            flex-wrap: wrap;
        }
        .score-card {
            background-color: #f8f9fa;
            border-radius: 12px;
            padding: 20px;
            width: 180px;
            box-shadow: 0 4px 12px rgba(0,0,0,0.05);
            border: 1px solid #e9ecef;
        }
        .score-card h3 {
            margin: 0 0 10px;
            font-size: 16px;
            font-weight: 500;
            color: #555;
        }
        .score-card p {
            margin: 0;
            font-size: 28px;
            font-weight: 700;
            color: #333;
        }
        .score-details table {
            width: 100%;
            font-size: 16px;
        }
        .score-details td {
            padding: 4px 0;
        }
        .score-details td:last-child {
            text-align: right;
            font-weight: 700;
        }
        .report-actions button {
            background-color: #fff;
            border: 1px solid #ccc;
            border-radius: 8px;
            padding: 12px 25px;
            font-size: 16px;
            cursor: pointer;
            margin: 0 10px;
            transition: background-color 0.2s ease, border-color 0.2s ease, transform 0.2s ease;
        }
        .report-actions button:hover {
            background-color: #f1f1f1;
            border-color: #bbb;
            transform: translateY(-2px);
        }
        .report-actions button.primary {
            background-color: #28a745;
            color: white;
            border-color: #28a745;
        }
        .report-actions button.primary:hover {
            background-color: #218838;
        }
        
        .hint-container {
            background-color: #e0f7fa;
            border: 1px solid #b2ebf2;
            border-radius: 8px;
            padding: 15px;
            margin-top: 20px;
            color: #006064;
            font-size: 15px;
            line-height: 1.6;
            display: none; /* 默认隐藏 */
        }
      </style>
    </head>
    <body>
      <div class="main-wrapper">
          <div class="quiz-container">
            <div class="quiz-header">
              <h1>优化高并发场景下的数据库查询性能 - 交互式测验</h1>
              <p>检验你对文档内容的理解程度</p>
            </div>
            <div id="quiz-content">
                <div class="quiz-body">
                    <div class="progress-bar">
                        <div id="progress-indicator"></div>
                    </div>
                    <div id="question-container">
                      <p id="question-text"></p>
                      <ul class="options-list" id="options-list"></ul>
                    </div>
                    <div id="result-container"></div>
                    <div id="hint-container" class="hint-container"></div>
                </div>
                <div class="quiz-footer" id="quiz-footer">
                  <button id="prev-btn" class="nav-btn">上一题</button>
                  <button id="hint-btn" class="nav-btn" style="background-color: #ffc107; color: #333; box-shadow: 0 4px 12px rgba(255,193,7,0.3);">提示</button>
                  <button id="next-btn" class="nav-btn">下一题</button>
                </div>
            </div>
          </div>
      </div>

      <script>
        const quizData = [
  {
    "question": "在进行数据库性能瓶颈分析时，监控“慢查询日志”的主要目的是什么？",
    "options": [
      "监控数据库的CPU和内存使用率。",
      "记录所有成功的数据库连接请求。",
      "识别并分析执行时间超过预设阈值的查询语句，以找出潜在的性能问题。",
      "统计单位时间内数据库处理的总查询数量。"
    ],
    "correctAnswerIndex": 2,
    "explanation": "慢查询日志是专门用来记录执行时间过长的SQL查询的。通过分析这些日志，开发人员和DBA可以精确定位到效率低下的查询，并对其进行优化，例如添加索引或重写SQL，这是性能瓶颈分析中非常关键的一步。",
    "source": "文档中「分析性能瓶颈」->「2. 监控数据库性能指标」部分",
    "hint": "文档提到，这个日志可以帮助分析哪些查询占用了较长的时间。"
  },
  {
    "question": "某电商系统为提升数据库并发处理能力，决定将用户相关的表（如`users`, `user_profiles`）和订单相关的表（如`orders`, `order_details`）分别存放到不同的数据库实例中。这种架构优化策略被称为？",
    "options": [
      "水平分库",
      "垂直分库",
      "读写分离",
      "垂直分表"
    ],
    "correctAnswerIndex": 1,
    "explanation": "垂直分库是根据业务模块或功能，将不同业务的数据表拆分到不同的数据库中。这种方式适用于业务逻辑之间耦合度较低的场景，可以有效分散不同业务模块的数据库压力。",
    "source": "文档中「数据库架构优化」->「1. 数据库分库分表」->「1.1 分库」部分",
    "hint": "思考一下，这种拆分是基于“业务功能”还是基于“数据范围”？"
  },
  {
    "question": "在高并发场景下，为了防止大量缓存项在同一时间失效，导致所有请求瞬间涌向数据库，造成数据库压力剧增，应该采用哪种策略来应对这种“缓存雪崩”问题？",
    "options": [
      "使用布隆过滤器过滤无效请求。",
      "对所有缓存数据设置相同的、较短的过期时间。",
      "为缓存的过期时间增加一个随机值，使其分散失效。",
      "当缓存未命中时，直接缓存一个空值（null）。"
    ],
    "correctAnswerIndex": 2,
    "explanation": "为了避免缓存雪崩，一个有效的策略是给缓存的过期时间加上一个随机数，这样可以确保缓存不会在同一时刻大规模集中失效，从而将数据库的访问压力平摊到更长的时间窗口内。缓存空值和布隆过滤器是解决“缓存穿透”问题的方法。",
    "source": "文档中「数据库架构优化」->「3. 数据库缓存优化」->「3.2 缓存穿透与缓存雪崩」部分",
    "hint": "文档中提到“大量缓存同时过期”的问题，并给出了相应的解决方案。"
  },
  {
    "question": "在创建联合索引（Composite Index）时，字段的顺序至关重要。以下关于联合索引字段顺序的优化策略，哪一项是正确的？",
    "options": [
      "应将数据类型为字符串的字段放在最前面。",
      "应将字段按照字母顺序进行排列。",
      "应将选择性（Selectivity）最低的字段放在最前面。",
      "应将查询条件中最常使用的字段放在联合索引的最前面。"
    ],
    "correctAnswerIndex": 3,
    "explanation": "联合索引遵循“最左前缀匹配”原则。为了最大化索引的利用率，应该将查询条件中最常用、过滤性最好的字段放在索引定义的最左边。这样，更多的查询可以有效地利用到这个索引。",
    "source": "文档中「索引优化」->「2. 索引优化策略」->「2.4 联合索引的顺序优化」部分",
    "hint": "联合索引的效率与查询条件中字段的使用频率有关。"
  },
  {
    "question": "为什么在优化查询语句时，文档强烈建议避免使用 `SELECT *` ？",
    "options": [
      "因为它会阻止数据库使用任何索引。",
      "因为它会增加数据库的写操作负担。",
      "因为它会返回所有列的数据，即使很多列是不需要的，从而增加网络开销和应用内存消耗。",
      "因为它会导致事务隔离级别自动降级。"
    ],
    "correctAnswerIndex": 2,
    "explanation": "使用 `SELECT *` 会查询出表中的所有字段，即使应用层只用到了其中一两个字段。这不仅会增加数据库的I/O负担，还会占用不必要的网络带宽，并增加应用服务器的内存消耗。明确指定需要的列是查询优化的基本原则之一。",
    "source": "文档中「优化查询语句」->「3. 减少返回的数据量」部分",
    "hint": "考虑一下查询所有字段对数据传输量和内存的影响。"
  },
  {
    "question": "在数据库连接池的配置中，如果将“最大连接数（maxTotal）”设置得过高，可能会带来什么风险？",
    "options": [
      "导致应用获取连接时频繁超时。",
      "增加数据库服务器自身的CPU和内存负载，可能影响其整体性能。",
      "会使数据库连接频繁创建和销毁，降低效率。",
      "无法有效利用数据库缓存。"
    ],
    "correctAnswerIndex": 1,
    "explanation": "虽然连接池可以提高性能，但每个数据库连接都会消耗数据库服务器的资源（如内存和CPU）。如果最大连接数设置得过高，超出了数据库的处理能力，反而会因为过度的资源竞争和上下文切换，导致数据库性能下降。",
    "source": "文档中「数据库连接优化」->「2. 合理配置连接池参数」部分",
    "hint": "思考一下，每个数据库连接在数据库服务端意味着什么？"
  },
  {
    "question": "在一个读多写少、且数据冲突概率较低的业务场景中，为了提升并发性能，应该优先选择哪种锁策略？",
    "options": [
      "悲观锁（Pessimistic Locking）",
      "表级锁（Table-level Lock）",
      "乐观锁（Optimistic Locking）",
      "串行化隔离级别（Serializable）"
    ],
    "correctAnswerIndex": 2,
    "explanation": "乐观锁假设数据冲突的概率很低，因此在数据操作时不加锁，只在提交更新时通过版本号或时间戳等机制检查数据是否被其他事务修改。这种方式避免了加锁带来的性能开销，非常适合读多写少、冲突概率低的场景。",
    "source": "文档中「事务与锁优化」->「2. 锁的优化」->「2.1 锁粒度优化」部分",
    "hint": "哪种锁机制是在提交时才检查冲突，而不是在操作前就加锁？"
  },
  {
    "question": "以下哪个SQL查询的WHERE子句最有可能导致 `create_time` 字段上的索引失效？",
    "options": [
      "WHERE create_time > '2024-01-01'",
      "WHERE create_time IN ('2024-01-01', '2024-02-01')",
      "WHERE YEAR(create_time) = 2024",
      "WHERE create_time = '2024-05-20'"
    ],
    "correctAnswerIndex": 2,
    "explanation": "在索引字段上使用函数（如 `YEAR()`）或进行计算，会导致数据库优化器无法使用该字段的索引，从而退化为全表扫描。为了利用索引，应将查询条件改写为范围查询，例如 `WHERE create_time >= '2024-01-01' AND create_time < '2025-01-01'`。",
    "source": "文档中「索引优化」->「3. 索引优化的常见问题与解决方案」->「3.1 索引失效」部分",
    "hint": "文档中提到“在索引字段上进行了运算或函数操作”会导致索引失效。"
  }
];
        console.log("Quiz Data:", JSON.parse(JSON.stringify(quizData))); // 添加这行用于调试，以可展开的JSON格式输出
        
        let currentQuestionIndex = 0;
        let score = 0;
        // 存储每个问题的回答状态
        const userAnswers = new Array(quizData.length).fill(null); 

        const questionTextEl = document.getElementById('question-text');
        const optionsListEl = document.getElementById('options-list');
        const resultContainerEl = document.getElementById('result-container');
        const quizContentEl = document.getElementById('quiz-content');
        const progressIndicatorEl = document.getElementById('progress-indicator');
        const prevBtn = document.getElementById('prev-btn');
        const nextBtn = document.getElementById('next-btn');
        const hintBtn = document.getElementById('hint-btn');
        const hintContainerEl = document.getElementById('hint-container');

        function loadQuestion() {
          resultContainerEl.innerHTML = '';
          optionsListEl.innerHTML = '';
          hintContainerEl.style.display = 'none'; // 隐藏提示
          
          if (currentQuestionIndex >= quizData.length) {
            showFinalScore();
            return;
          }

          updateProgress();

          const currentQuestion = quizData[currentQuestionIndex];
          questionTextEl.textContent = `(${currentQuestionIndex + 1}/${quizData.length}) ${currentQuestion.question}`;
          
          currentQuestion.options.forEach((optionText, index) => {
            const li = document.createElement('li');
            li.className = 'option-item';
            li.textContent = optionText;
            li.dataset.index = index; // Store index in a data attribute
            // 如果这道题已经回答过，恢复状态
            if (userAnswers[currentQuestionIndex] !== null) {
                if (index === userAnswers[currentQuestionIndex]) {
                    li.classList.add('selected');
                }
            }
            optionsListEl.appendChild(li);
          });

          // 如果已经回答过，直接显示结果
          if (userAnswers[currentQuestionIndex] !== null) {
              const isCorrect = userAnswers[currentQuestionIndex] === currentQuestion.correctAnswerIndex;
              showResult(isCorrect, currentQuestion);
          }
          
          updateNavigationButtons();
          updateProgress();
        }

        function selectOption(optionIndex) {
            userAnswers[currentQuestionIndex] = optionIndex;
            const currentQuestion = quizData[currentQuestionIndex];
            const isCorrect = optionIndex === currentQuestion.correctAnswerIndex;

            // 重新计算分数
            score = userAnswers.reduce((acc, answer, index) => {
                return answer === quizData[index].correctAnswerIndex ? acc + 1 : acc;
            }, 0);

            showResult(isCorrect, currentQuestion);
            updateNavigationButtons();
        }
        
        function updateProgress() {
            const answeredQuestions = userAnswers.filter(answer => answer !== null).length;
            const progressPercentage = (answeredQuestions / quizData.length) * 100;
            progressIndicatorEl.style.width = `${progressPercentage}%`;
        }
        
        function updateNavigationButtons() {
            prevBtn.style.display = 'block';
            nextBtn.style.display = 'block';
            hintBtn.style.display = 'block'; // 显示提示按钮

            prevBtn.disabled = currentQuestionIndex === 0;
            nextBtn.disabled = false; // 最后一题时，下一题按钮不禁用，而是用于显示报告
            nextBtn.textContent = (currentQuestionIndex === quizData.length - 1) ? '查看报告' : '下一题';
            
            // 如果当前问题没有提示，则禁用提示按钮并隐藏提示内容
            if (!quizData[currentQuestionIndex].hint) {
                hintBtn.disabled = true;
                hintContainerEl.style.display = 'none';
                hintContainerEl.textContent = ''; // 清除旧的提示内容
            } else {
                hintBtn.disabled = false;
            }
        }

        function showResult(isCorrect, questionData) {
            resultContainerEl.innerHTML = ''; // 清空之前的结果
            const resultBox = document.createElement('div');
            resultBox.className = `result-box ${isCorrect ? 'correct' : 'incorrect'}`;
            
            let html = `<h3>${isCorrect ? '回答正确！' : '回答错误'}</h3>`;
            if (!isCorrect) {
                html += `<p><strong>正确答案是：</strong> ${questionData.options[questionData.correctAnswerIndex]}</p>`;
            }
            html += `<div class="explanation-text">${questionData.explanation}</div>`;
            html += `<div class="source-text">来源: ${questionData.source}</div>`;
            
            resultBox.innerHTML = html;
            resultContainerEl.appendChild(resultBox);

            // 禁用所有选项的点击事件，并高亮正确/错误答案
            Array.from(optionsListEl.children).forEach((child, index) => {
                child.style.pointerEvents = 'none';
                // 高亮正确答案
                if (index === questionData.correctAnswerIndex) {
                    child.classList.add('correct'); // 需要添加CSS样式
                    child.style.backgroundColor = '#d4edda';
                    child.style.borderColor = '#c3e6cb';
                }
                // 如果选错了，高亮错误选项
                if (!isCorrect && index === userAnswers[currentQuestionIndex]) {
                    child.classList.add('incorrect'); // 需要添加CSS样式
                    child.style.backgroundColor = '#f8d7da';
                    child.style.borderColor = '#f5c6cb';
                }
            });
        }

        function goToNextQuestion() {
            if (currentQuestionIndex < quizData.length - 1) {
                currentQuestionIndex++;
                loadQuestion();
            } else {
                showFinalScore();
            }
        }

        function goToPreviousQuestion() {
            if (currentQuestionIndex > 0) {
                currentQuestionIndex--;
                loadQuestion();
            }
        }
        
        function showHint() {
            const currentQuestion = quizData[currentQuestionIndex];
            if (currentQuestion.hint) {
                hintContainerEl.textContent = currentQuestion.hint;
                hintContainerEl.style.display = 'block';
            } else {
                hintContainerEl.style.display = 'none';
            }
        }

        function showFinalScore() {
            document.querySelector('.quiz-body').style.display = 'none';
            document.getElementById('quiz-footer').style.display = 'none';

            const correctCount = score;
            const totalQuestions = quizData.length;
            const answeredCount = userAnswers.filter(a => a !== null).length;
            const wrongCount = answeredCount - correctCount;
            const skippedCount = totalQuestions - answeredCount;
            const accuracy = totalQuestions > 0 ? Math.round((correctCount / totalQuestions) * 100) : 0;
            const errorRate = totalQuestions > 0 ? Math.round((wrongCount / totalQuestions) * 100) : 0;

            const finalScoreHtml =
                '<div class="final-score-container">' +
                '<h2>答题报告</h2>' +
                '<div class="score-summary">' +
                '<div class="score-card">' +
                '<h3>得分</h3>' +
                '<p>' + correctCount + ' / ' + totalQuestions + '</p>' +
                '</div>' +
                '<div class="score-card">' +
                '<h3>正确率</h3>' +
                '<p>' + accuracy + '%</p>' +
                '</div>' +
                '<div class="score-card">' +
                '<h3>错误率</h3>' +
                '<p>' + errorRate + '%</p>' +
                '</div>' +
                '<div class="score-card score-details">' +
                '<table>' +
                '<tr><td>正确</td><td>' + correctCount + '</td></tr>' +
                '<tr><td>错误</td><td>' + wrongCount + '</td></tr>' +
                '<tr><td>未答</td><td>' + skippedCount + '</td></tr>' +
                '</table>' +
                '</div>' +
                '</div>' +
                '<div class="report-actions">' +
                '<button id="review-btn">回顾测验</button>' +
                '<button class="primary" onclick="location.reload()">再试一次</button>' +
                '</div>' +
                '</div>';

            let reportEl = document.querySelector('.final-score-container');
            if (reportEl) {
                reportEl.remove();
            }
            quizContentEl.insertAdjacentHTML('beforeend', finalScoreHtml);
            document.getElementById('review-btn').addEventListener('click', reviewQuiz);
        }

        function reviewQuiz() {
            const reportEl = document.querySelector('.final-score-container');
            if (reportEl) {
                reportEl.remove();
            }

            document.querySelector('.quiz-body').style.display = 'block';
            document.getElementById('quiz-footer').style.display = 'flex';
            
            currentQuestionIndex = 0;
            loadQuestion();
            updateNavigationButtons(); // Ensure nav buttons are correctly displayed
        }

        // Event Delegation for options
        optionsListEl.addEventListener('click', (event) => {
            if (event.target && event.target.matches('li.option-item')) {
                // Check if the question has already been answered
                if (userAnswers[currentQuestionIndex] === null) {
                    const selectedIndex = parseInt(event.target.dataset.index, 10);
                    selectOption(selectedIndex);
                }
            }
        });

        prevBtn.addEventListener('click', goToPreviousQuestion);
        nextBtn.addEventListener('click', goToNextQuestion);
        hintBtn.addEventListener('click', showHint);
        
        // 初始加载
        loadQuestion();
      </script>
    </body>
    </html>
  